This invention relates to hoses that are stable in length under the effect of an internal pressure.
This invention relates particularly to hoses for transporting fluids under pressure, such as in particular hydrocarbons produced during operation of underwater wells.
The applicant company produces and markets, in great lengths, such hoses which exhibit high mechanical properties, particularly tensile strength, resistance to crushing and to the internal pressure of the transported fluid.
Thus, the applicant company produces hoses essentially comprising an internal leak tightness sheath, an armoring with tensile strength usually made up of two crossed layers each consisting of wires placed spirally around the hose with the same sheathing angle, the wires of the two layers being wound with opposite angles relative to the axis of the hose, a pressure resistance armoring comprising one or more laYers of fastened strip or shapes wires wound by spiraling at an angle close to 90.degree. relative to the axis of the hose, and an external sheath. They are the "smooth-bore" type hoses.
The "rough bore" type hoses further comprise, under the internal leak tightness sheath, an armoring with resistance to crushing and to external pressure generally consisting of a helical winding with a slight pitch of one or more fastenable shapes, particularly steel strip.
In some cases the pressure resistance armoring is eliminated and the wires of the two armoring layers are then placed at the equilibrium angle, namely 55.degree. , relative to the axis of the hose.
ln some applications, particularly in the case where the hoses, used for collecting hydrocarbons produced by underwater wells, must be buried, i.e., placed at the bottom of a trench made in the the underwater bottom, it is essential to avoid a notable axial elongation of the hose in operation under the effect of the internal pressure of the fluid transported, because such an axial elongation causes a deformation of the hose, running the risk of bringing it out of the trench.
Attempts have been made to propose hoses exhibiting as slight an elongation as possible in operation under high internal pressure.
Thus, French Patent 2 557 254 describes a hose comprising an armoring with tensile strength consisting of at least one pair of sheathing layers generally laid with a sheathing angle between 15.degree. and 45.degree. relative to the axis of the hose and a pressure resistance armoring comprising one or more layers of spiraled wires. This document provides for using determined ratios between the rigidities of the wires of the spiral layers of the pressure resistance armoring and the layers of wires constituting the armoring with tensile strength.
In the usual case where all the wires are of the same material, for example steel, this ratio is reduced to a ratio of thickness.
If the moduli of elasticity of the wires of the spiraled layers of the wires of the layers of the armoring with tensile strength are identical, a high thickness ratio is obtained (between 2.5 and 8) between the armoring with tensile strength and the pressure resistance armoring, which notably increases the linear weight of the hose, and therefore, its cost.
Further, it is not possible to benefit fully from the speed of the operation of the armoring machines which in practice is clearly greater than the speed of operation of a spiraling machine.
Moreover, it has been proposed in French Patent 2 464 423 to use an armoring consisting of a plurality of pairs of crossed layers of sheathing wires. However, this document does not give any constructive solution to assure dimensional stability particularly in the axial direction of the hose under the action of an internal pressure. Further, there is provided the presence of one or more pairs of layers wound at an angle of 90.degree. relative to the axis of the hose, i.e., it is a case of spiraled wires with the drawbacks mentioned above.
The studies conducted by the applicant company show that when a hose is put under internal pressure two stages of axial deformation successively occur.
First, for a relatively slight rise in pressure, for example, up to 5 MPa, a relatively large axial deformation is noted, occurring inevitably from the existence of manufacturing plays between the layers of the armoring wires and from the fact of the deformation of the filling materials optionally placed between the armoring layers.
If particular constructive measures are not provided, a subsequent deformation phase then occurs which can be considerable when the internal pressure is high which is the case in practical applications where the operating pressures can reach values of several tens of MPa that is, in the range of 10-14 100 MPa.